Steam or vapor generator having at least two firing systems



P. PROFOS 3,017,870

STEAM OR VAPOR GENERATOR HAVING AT LEAST TWO FIRING SYSTEMS Jan. 23, 1962 2 Sheets-Sheet 1 Filed March 12. 1959 Inventor: PquL Pmoros.

Jan. 23, 1962 P. PROFOS 3,017,870

STEAM OR VAPOR GENERATOR HAVING AT LEAST TWO FIRING SYSTEMS Filed March 12, 1959 2 Sheets-Sheet 2 rate The present invention relates to a steam or vapor generator having at least two firing systems, each firing systern supplying heat to a heating surface system through which a portion of the operating medium is conducted, a first one of said heating surface systems including a reheater and a second of said heating surface systems including final superheaters.

The second heating surface system includes separate superheater sections one of which receives vaporized operating medium only from the first heating surface system, the second section receiving vaporized medium only from the second heating surface system.

In the first heating surface system preferably a preliminary superheater is arranged from which superheated vapor is conducted into the final superheater which forms part of the second heating surface system. The outlet temperature of the final superheater is controlled by injecting liquid operating medium into the vapor while it passes from the preliminary superheater into the final superheater.

The temperature of the vapor leaving the reheater is preferably controlled by directing heat energy produced by the first firing system in a first combustion chamber more or less directly onto the reheater which forms part of the first heating surface system.

The novel features which are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, and additional objects and advantages thereof will best be understood from the following description of an embodiment thereof when read in connection with the accompanying drawing, in which:

FIG. 1 is a diagrammatic illustration of a steam generator according to the invention.

FIG. 2 is a diagrammatic illustration of a control mechanism for the steam generator shown in FIG. 1.

FIG. 3 is a diagrammatic illustration of an example of a temperature measuring device used in the apparatus illustrated in FIG. 2.

Referring more particularly to FIG. 1 of the drawing, numerals I and II designate two individual combustion chambers firing, and heating surface systems. The system I is supplied with liquid operating medium, for example water, by a feed pump 13 from a feedwater reservoir 11 through a conduit 12 in which a feedwater control valve 14 is inteiposed. The water passes through a conventional water preheater 15 which may be heated by flue gas, into an evaporator section 16 which may line the walls of a combustion chamber forming part of the system I. The steam produced in the evaporator 16 flows into a preliminary superheater 17 forming part of the system I and discharging superheated steam into a final superheater 18 forming part of the system II. The final superheater 18 is connected by live steam pipes 19 and 20 to the inlet of a high pressure turbine 43. The exhaust of the latter is conducted through a pipe 21 to a pipe 22 conducting the partly expanded steam into a reh-eater 23 forming part of the system I. The reheated steam flows through a pipe 24 into a low pressure turblue 25 from which the expanded steam flows into a condenser 26. The reheater can be by-passed by conducting steam from the pipe 21 through a pipe 27 in which a valve 28 in interposed. The condensate formed in the condenser 26 is returned by a condensate pump 30 through pipes 29 and 31 to the reservoir 11. One or more feedwater preheaters 32, of which only one is shown, are interposed in the conduit 31 which may be heated by steam tapped from a turbine in the conventional manner, not shown.

The system II is supplied with water by a pump 36 through a pipe 35 from the reservoir 11. A feedwater control valve 37 is interposed in the pipe 35 downstream of the pump 36. The water flows through an economizer 33 into an evaporator 39 whose tubes may line the Wall of the combustion chamber of the system II. The evaporated operating medium flows into a preliminary superheater 40 and therefrom into a final superheater 41. The thus produced live steam passes through a pipe 42 into the pipe 20, is partly expanded in the turbine 43, and conducted through the pipes 2 1 and 22 to the reheater 23 in the system I.

The combustion chambers of the systems I and II are individually heated by tilting burners 51 and 52. Usually there is a plurality of such burners in each combustion chamber, one only being shown for convenience. The burner 51 is supplied with fuel through a pipe 53 in which a fuel control valve 54 is interposed. The burner 52 receives fuel through a pipe 55 which is controlled by a valve 56. Oil or pulverized coal may serve as fuel. For simplicitys sake no combustion air supply devices are shown, conventional devices including primary and secondary air supply means being used. By changing the positions of the tilting burners the distribution of the heat in the combustion chambers and heating surfaces supplied thereby may be changed. Tilting of the burners 51 and 52 is effected by motor operators 57 and 58, respectively, which are suitably connected to the burners.

Valves 61 and 62 are arranged in the pipes 19 and 42, respectively, which valves may be controlled in the conventional manner according to the pressure downstream of the valves and/or by a speed governor of the turbine 43. Upstream of the valves 61 and 62 by-pass pipes 63, 64, respectively, are connected to the pipes 19 and 42, respectively, the by-pass pipes conducting steam into the reservoir 11 through pipes 64 and 63, respectively, provided with valves 65 and 66, respectively.

The steam generator is controlled by a control apparatus which will now be described. The amount of feedwater supplied to the evaporator 16 of the system I is controlled according to the average temperature of the operating medium which is measured by a temperature sensing device 71 at the inlet of the preliminary superheater 17. The device 71 produces a signal which is transmitted through a conductor 72 to a conventional motor operator for the feedwater control valve 14. Reduction of the temperature below a set value causes closing of the valve 14 and vice versa. A like feedwater control system is provided in the system II wherein a temperature sensing device 73 produces a signal which is transmitted through a conductor 74 to a motor operator of the valve 37.

The amount of fuel supplied to the tilting burner 51 of the system I is controlled by the valve 54 whose motor operator responds to signals produced by a pressure sensitive device 75 in the pipe 1?. If the pressure drops below a set value the fuel supply is increased and vice versa. The signals are transmitted by a conductor 76 interconnecting the device 75 and the motor operator of the valve 54, The amount of fuel supplied to the burner 52 of the system H is regulated in like manner. A device 77 responsive to the pressure in the pipe 42 produces a signal which is transmitted through a conductor 78 to the motor operator of the valve 56. A drop of the pressure below a set value increases the fuel supply and vice versa.

The temperature of the steam leaving the reheater 23 is controlled by changing the position of the tilting burner 51. A temperature sensing device 79 is arranged in the pipe 24 which device produces a signal transmitted through a conductor 80 to the motor operator 57 of the burner 51. Upon a reduction of the temperature of the reheated steam below an adjustable value, the motor operator rocks the burner in the direction of the arrow 81 whereas an increase of the superheat temperature causes rocking of the burner 51 in the direction of the arrow 31.

The temperature of the steam leaving the final superheater 18 is controlled by injecting water into a conduit connecting the outlet of the preliminary superheater 17 to the inlet of the finalsuperheater 18. A temperature sensing device 83 is arranged in the pipe 19 for producing a signal which is transmitted through a conductor 84 to a motor operator for a water injection valve 85. The latter is interposed in a pipe 86 terminating at. 82 in the pipe interconnecting the superheater sections 17 and 18. The pipe 86 is supplied with feedwater under pressure in the conventional manner. The elements 83 and 86 cooperate so that an increase of the live steam temperature in the pipe 19 above a set value increases the amount of water injected at the point 82 and vice versa.

For controlling the like steam temperature leaving the superheater 41 the position of the tilting burner 52 is changed. A temperature measuring device 87 is arranged in the live'steam pipe 42 for producing a signal which is transmitted through a conductor 88 to a motor operator 58 for rocking the burner 52 so that, if the live steam temperature drops below an adjustable set value more heat is directed toward the superheater 41 and vice versa.

In FIGS. 1 and 2 the same numerals are used for designating like elements. A temperature sensing device 91 is arranged in the connection between the evaporator 16 and the preliminary superheater 17 for controlling the feedwater supplied to the system I. The device 91 may be a conventional liquid thermometer (FIG. 3) including a bulb 92 placed inside the tube connecting the evaporator 16 to the preliminary superheater 17 and exposed to the steam flowing therein. The bulb 92 which communicates through a pipe 93 with bellows 94- is filled with a vaporizable liquid whose vapor pressure corresponds to the temperature of the steam flowing past the bulb 92. An increase of this pressure causes an elongation of the bellows 94 and a downward movement of a pilot valve 95 so that a piston forming part of a motor operator 96 for the feedwater control valve 14 is moved in upward direction whereby the flow area of the valve 14 is increased. A proportionalintegral operation of the control apparatus iseflected by a dashpot device 97 and a spring 98 operatively connected to the motor operator 96. A drop of the temperature sensed by the device 91 causes a reduction of the flow area of the valve 14 and, consequently, a reduction of the amount of feedwater supplied to the system I.

The amount of feedwater supplied to the evaporator 39 of the system H, i.e. the feedwater control valve 37 of the system H,- is controlled in the same manner as the feedwater control valve 14 of the system I.

The amount of cooling water injected at the point 82 is controlled according to the temperature measured by the device 83 sensing the temperature of the live steam downstream of the final superheater 18. The temperature sensing device maybe of the type shown in FIG. 3, the pressure of the vapor generated in the bulb 92 acting through a pipe'99 on bellows 100 forming the motor operator for the water injection control valve 85. As a modification the energy produced by the bellows 100 may be amplified in an apparatus as used for actuating the feed valve 14 and including a yielding feedback.

For controlling the amount of fuel supplied to the burner 52 through the pipe 55 the pressure of the live steam in the pipe 42 is transmitted through a pipe 103 to. bellows 104 which is operatively connected to a pilot valve 106. Reduction of the steam pressure moves the pilot valve downward, effecting upward movement of a piston of a hydraulic servomotor 108 connected to and controlled by the pilot valve 106. Upward movement of the piston of the motor operator 108 effects opening of the. fuel valve 56. An increase of the steam pressure above a set value closes the valve 56 and reduces the amount of fuel supplied to the burner 52. The servomotor 108 is provided with a dashpot device 109 and a spring 110 for implying a proportional integral characteristic to the control apparatus.

The position of the rockable burner 52 is controlled according to the temperature measured by a temperature sensing device 87 which produces a pressure acting through a pipe 111 on bellows 112.which are connected and actuate a pilot valve 113 controlling the operation of a motor operator 58 for changing the position of the burner 52. A lowering of the live steam pressure measured by the device 87 causes swinging of the burner 52 in the +direction of the arrow 114 and vice versa. A dashpot device 131 and a spring 133 impart a proportional integral characteristic to the operation of the motor operator 58.

The position of the tilting burner 52 forming part of the system I is controlled in a similar manner as that of the burner 52. A thermometer 79 of the type shown in- FIG. 3 and arranged downstream of the of the outlet of the reheater 23 produces a pressure acting through a' pipe 115 on bellows 116 which actuates a pilot valve 117 controlling the hydraulic motor operator 57 which rocks the burner 51. A reduction of the reheat temperature effects an upward movement of the mouth of the burner 51 in the +direction of the arrow 81 and vice versa. A proportional integral characteristic of the just described control apparatus is effected by the provision of a dashpot device 132 and a spring 134.

For controlling the amount of fuel supplied to the burner 51 the live steam pressure at point 75 of the live steam pipe 19 is transmitted through a pipe 121 to belelows 122. An increasing pressure tends to elongate the bellows 122, thereby moving a pilot valve 123 opera-- tively connected to the bellows 122 for controlling a hydraulic motor operator 124 which actuates the fuelsupply valve 54 in the fuel line 53. This apparatus is provided with a yielding feedback including a dashpot 125 a spring 126. A reduction of the pressure of the live steam in the pipe 19 causes an increase of the flow area of the fuel control valve 54 and vice-versa.

The control apparatus as described above is provided with conventional set point adjusting devices which are not shown.

Thearrangement according to the invention affords starting of the firing system 11 before starting the system I. For starting the steam generator according to the invention the feed pump 36 and the burner 52 are started while the shutoff valve 62 (FIG. 1) in the live steam pipe 42 is closed. Water which is gradually heated and begins to evaporate is recirculated through the pipe 63 to the reservoir 11 until the temperature and the pressure of the steam in the live steam pipe 42 have reached the desired values. A small amount of steam may be conducted to the turbine 43 for heating the latter by slightly opening the valve 62. The latter is fully opened and thevalve 66 is fully closed when the steam pressure and: steam temperature have reached the desired values. The turbine 43 can now be brought up to normal speed. The exhaust of the turbine 43 may be conducted into the turbine 25 or may be by-passed around the turbine 25 through a pipe 128 and conducted into the condenser 26 by opening a bypass valve 127. This shows that the system H can be operated normally without operating the system I. For cooling the final superheater 18 a small amount of Water is pumped by the feed pump 13 or an auxiliary pump, not shown, through the tubes of the system 1 and returned through the pipe 64 to the reservoir 11. The valve 61 is closed and the valve 65 is open during this operation.

For starting the system I the tilting burner 51 is lighted and the feedwater pump 13 brought up to normal speed. When the temperature and the pressure of the live steam have reached the desired values, the valve 55 is closed and the valve 61 is opened. With the arrangement according to the invention steam is available for cooling the reheater 23 during the starting period of the system I because the system H is already in normal operation and steam exhausted by the turbine 43 can be passed through the reheater 23. Because of the temperature regulation of the live steam leaving the final superheater "it; by injecting water at the point 32 the reheat temperature of the steam can be controlled by properly positioning the tilting burner 51 without adversely alTecting the leve steam temperature in the pipe 19.

The invention is not limited to the described and illustrated examples. In lieu of the tilting burner a grate may be provided and the distribution of the heat energy be controlled by means of dampers. The illustrated and described mechanical-hydraulic control apparatus may be replaced by corresponding electric apparatuses.

The steam generator according to the invention can be operated at subcritical, critical or supercritical pressure of the operating medium. The invention can be applied to natural circulation steam boilers as well as to forced flow steam generators.

I claim:

1. A steam generator comprising two separate chambers, a separate fuel firing means in each of said chambers, two separate tube systems, separate means individually connected to said tube systems, for separately feeding water at a relatively high pressure into said tube systems, each tube system having a steam generating section having an inlet and a superheating section connected in series relation to said steam generating section with respect to the flow of the operating medium through the respective tube system and having an outlet, each of said tube systems forming a flow path for the operating medium from the respective inlet to the respective outlet, said flow paths being physically separated throughout the en tire lengths of the flow paths, the superheating section of one of said tube systems having a first superheater and a final superheater connected in series relation to said first superheater, and a reheater for reheating relatively low pressure steam, the entire reheater, the entire steam generating section and the entire first superheater of the first tube system being located in one of said chambers and adapted to receive heat exclusively from said fuel firing means in the first chamber, the entire final superheater of the first tube system and the entire second tube system being located in the second of said chambers to receive heat exclusively from said fuel firing means in the second chamber.

2. A steam generator as defined in claim 1 including cooling water injecting means connected to the superheating section of the first tube system between said first superheater and said final superheater, and temperature sensing means connected to the outlet of said final superheater of the first tube system and to said injecting means for actuating the latter to maintain a predetermined temperature of the steam leaving said final superheater of the first tube system.

3. A steam generator as defined in claim 1 including control means connected to the fuel firing means in the first chamber wherein said reheater is located for changing the heat supply by said last mentioned firing means to said reheater, and temperature sensing means connected to the outlet of said reheater and operatively connected to said control means for increasing the 'heat supply to said reheater upon a decrease of the temperature at the reheater outlet and vice versa.

4. A steam generating plant comprising at least two separate combustion chambers, fuel burning means in each of said combustion chambers, two separate combustion gas passages individually connected to said combustion chambers for receiving hot combustion gas therefrom, two separate tube systems, each tube system having an evaporating and a superheating section, said tube systems being independent of each other with respect to the flow of water and steam therethrough, one of said tube systems being entirely located in one of said combustion chambers and in the gas passage connected thereto, the evaporating section of the second tube system being located in the second combustion chamber, the superheating section of the second tube system having a first superheater entirely located in the gas passage which is connected to the second combustion chamber, the superheating section of the second tube system having a final superheater connected in series relation to said first superheater and entirely located in the gas passage connected to the firs-t combustion chamber, a tubular steam reheater located in the gas passage connected to the second combustion chamber, temperature control means connected to the superheating section of said second tube system for controlling the temperature of the steam leaving said final superheater, and temperature control means connected to said reheater and to said fuel burning means in the second combustion chamber for controlling the temperature of the steam leaving said reheater independently of the temperature control of the superheating section of the second tube system.

References Cited in the file of this patent UNITED STATES PATENTS 2,752,899 Kasak July 3, 1956 2,781,746 Armacost et al Feb. 19, 1957 2,856,906 Armacost Oct. 21, 1958 2,872,907 Smith et al Feb. 10, 1959 2,896,592 Heller et al July 28, 1959 2,901,887 Buri Sept. 9, 1959 

